PCI/ERR: Recognize disconnected devices in report_error_detected()

PCI/ERR: Recognize disconnected devices in report_error_detected()

When a device is already unplugged by pciehp by the time the AER handler is
invoked, the PCIe device will already be in the pci_channel_io_perm_failure
state.  In that case simply return PCI_ERS_RESULT_DISCONNECT instead of
trying to do a state transition that will fail.

Also untangle the state transition failure from the lack of methods to
improve the debugging output in case it happens again.

Link: https://lore.kernel.org/r/20220601074024.3481035-1-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>